1. Field of the Invention
The present invention relates to a technique for an overcurrent limitation and output short-circuit protection circuit of a voltage regulator and, in particular, to an overcurrent protection and output short-circuit protection circuit that is easily designed and capable of being realized by a small circuit with low power consumption, a voltage regulator using the overcurent limitation and output short-circuit protection circuit, and various electronic equipment items such as mobile electronic devices including mobile phones, in-vehicle electric components, and home electric appliances.
2. Description of the Related Art
As overcurrent protection circuits of a power supply circuit, for example, disclosures in JP-A-2006-178539 (Patent Document 1) and JP-B2-3782726 (Patent Document 2) have been proposed.
JP-A-2006-178539 (Patent Document 1) discloses a technique for protecting an IC (Integrated Circuit) with a current limitation mode and a fold-back mode created by two circuit configurations of an overcurrent protection circuit and a short-circuit current protection circuit that set a maximum current value and a short-circuit current value, respectively.
In Patent Document 1, the fold-back mode of the short-circuit current protection circuit requires phase compensation. However, it is difficult to design the phase compensation in consideration of variations in manufacturing.
JP-B2-3782726 (Patent Document 2) discloses a technique for controlling a switching unit based on an output voltage at the time of supplying a current, thereby validating or invalidating a current voltage conversion unit that converts the output current of a proportional output current generation unit into a voltage.
Patent Document 2 is similar to the present invention in that the switching unit is controlled based on the output voltage at the time of supplying the current. When the output current of the proportional output current generation unit is attempted to be fed to an output node via the current voltage conversion unit so as to prevent the same from being invalidated, an IC (Integrated Circuit) having an output current of several hundred mA is effective because it is capable of making the resistance value of the switching unit much smaller than the resistance value of the current voltage conversion unit. However, in the case of an IC having an output current of 1 A or larger, the area of the switching unit disadvantageously becomes large so as to make the resistance value of the switching unit much smaller than the resistance value of the current voltage conversion unit.    Patent Document 1: JP-A-2006-178539    Patent Document 2: JP-B2-3782726
FIG. 1 is a diagram showing examples of an overcurrent protection circuit and an output short-circuit protection circuit of a conventional voltage regulator, and FIG. 2 is a graph showing the characteristics of an output current and an output voltage in the voltage regulator. An overcurrent protection circuit 1 in FIG. 1 determines the current limitation mode and the value of Imax in FIG. 2. On the other hand, the output short-circuit protection circuit 1 in FIG. 1 determines the fold-back mode and the value of Ishort in FIG. 2.
The circuit of a conventional voltage regulator is complicated because it requires the overcurrent protection circuit and the output short-circuit protection circuit. In addition, it is difficult to design the voltage regulator because the fold-back mode of the output short-circuit protection circuit requires the phase compensation.
Moreover, the voltage regulator requires the proportional output current generation units that generate a current proportional to a current flowing to an output transistor M1 (namely, a proportional output current generation unit M2 for the overcurrent protection circuit and a proportional output current generation unit M3 for the output short-circuit protection circuit) for each of the overcurrent protection circuit and the output short-circuit protection circuit. The output current of the proportional output current generation unit M2 for the overcurrent protection circuit and that of the proportional output current generation unit M3 for the output short-circuit protection circuit are fed to ground via their current voltage conversion units (namely, a current voltage conversion unit R2 for the overcurrent protection circuit and a current voltage conversion unit R3 for the output short-circuit protection circuit). Therefore, as the output current of the output transistor M1 increases, the power consumption of the IC increases proportionately.
Accordingly, an overcurrent protection and output short-circuit protection circuit of the voltage regulator is desired that solves the above deficiencies, achieves the overcurrent protection and the short-circuit current protection with a single current limitation circuit, is easily designed at low cost and capable of being realized by a small circuit with low power consumption.